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WHAT CAUSES THE SEASONS AND ASSOCIATED CHANGES IN INSOLATION?
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WHAT CAUSES THE SEASONS AND SSOCIATED CHANGES IN INSOLATION
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Transcript of WHAT CAUSES THE SEASONS AND ASSOCIATED CHANGES IN INSOLATION?
WHAT CAUSES THE SEASONS ANDASSOCIATED CHANGES IN INSOLATION?
SUN
December 22 June 21
September 21
March 21
Sun on horizon z = 90°
Sun on horizon z = 90°
March & September 21
SUN
Sun overhead z = 0°
N
Equator 0°
Antarctic Circle 66.5°S
Tropic ofCancer 23.5°N
Arctic Circle 66.5°N
Tropic ofCapricorn 23.5 °S
S
Noon z = Lat
WHAT DO WE KNOW SO FAR?
Zenith Angle at noon on these twodays is exactly equal to a location’sLatitude.
Gainesville, 29.5°NSouthampton, 52°NPerth, W.A., 32°S
Old SchoolGeography
N
March & September 21
SUN
Sun overhead z = 0°Equator
Antarctic C.
Cancer
Arctic C.
Capricorn
S
WHAT IS THE SUB-SOLAR POINT?
Sub-solar point is the latitude at which the noon day Sun appears directly overhead (z=0) at noon.
WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?
WHAT IS THE ZENITH ANGLE AT NOON ANYWHERE IN THE WORLD?
Z = LATITUDE OF LOCATION – LATITUDE OF SUB-SOLAR POINT
Thus on March and September 21:Z at Noon = Latitude of location - 0
WHAT IS THE SUB-SOLAR POINT FOR ANY DAY OF THE YEAR?
ANALEMMA
Latit
ude
of S
ub-s
olar
poi
nt
Equator
23.5°N
23.5°S
WHAT THE *%$* ?
SUN
December 22 June 21
September 21
March 21
N
S
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N Equator: z = 23.5°
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHERE IS THE SUN OVERHEAD (z=0) AT NOON?
23.5°N
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHAT IS NOONTIME Z IN GAINESVILLE?
Lat = 29.5°
Z = <29.5°= 29.5 – 23.5 = 6°
Small Zenith Angle: Sun Close ToOverhead – Higher Proportion ofSolar Constant – More Energy – HOT!
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHAT IS NOONTIME Z IN SOUTHAMPTON?
Lat = 52°N
Z = <52°= 52 – 23.5 = 28.5°
Small Zenith Angle: Sun Closer ToOverhead – Higher Proportion ofSolar Constant – More Energy – WARM!
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
June 21
SUN Sun overhead z = 0°
EquatorCancer
Antarctic
S
U
N
WHAT IS NOONTIME Z IN PERTH, W.A.?
Lat = 32°SZ = >32°
= 32 + 23.5 = 8.5°
Large Zenith Angle: Sun Further FromOverhead – Lower Proportion ofSolar Constant – Less Energy – COOLER!
SUN
December 22 June 21
September 21
March 21
N
S
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
N
Z = >0°= 0 + 23.5 = 23.5°
WHERE IS THE SUN OVERHEAD AT NOON?
23.5°S
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
N
Z = >29.5°= 29.5 + 23.5 = 53°
WHAT IS ZENITH ANGLE AT GAINESVILLE?
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
N
Z = >52°= 52 + 23.5 = 75.5°
WHAT IS ZENITH ANGLE AT SOUTHAMPTON?
N
s
Sun on horizon z = 90°
Sun on horizon z = 90°
December 22
Sun overhead z = 0°
Equator
Capricorn
Arctic SUN
S
U
NZ = < 32°= 32 - 23.5 = 23.5°
WHAT IS ZENITH ANGLE AT PERTH, W.A.?
WHAT IS THE SUB-SOLAR POINT TODAY?La
titud
e of
Sub
-sol
ar p
oint
Equator
23.5°S
21.5°S
Gainesville latitude ~ 29.5°NZ = 29.5 + 21.5 = 51°
BOTTOM LINE
BOTTOM LINE
March and September:Z at noon – Lat.
BOTTOM LINE
March and September:Z at noon = Lat.
Summer (Jun. in N, Dec. in S):Z at noon = Lat -23.5°
BOTTOM LINE
March and September:Z at noon = Lat.
Summer (Jun. in N, Dec. in S):Z at noon = Lat -23.5°
Winter (Dec. in N, Jun. in S):Z at noon = Lat +23.5°
